In wireless networks, an exposed node problem, or an exposed terminal problem occurs when a node is prevented from sending packets to other nodes because of a neighboring transmitter. FIG. 1 is a schematic diagram of a scenario of exposed nodes in an existing network. As shown in FIG. 1, there are 4 nodes T1, R1, T2 and R2 in the network The receivers R1 and R2 are out of range of each other, yet the transmitters T1 and T2 in the middle are in range of each other. Here, if data transmission between T1 and R1 is taking place, node T2 is prevented from transmitting data to R2 as it concludes after carrier sense that it will interfere with the data transmission by its neighbor T1.
However, in such a case, R2 could still receive the data transmission from T2 without interference because it is out of range of T1. In the example shown in FIG. 1, node T1 and T2 are exposed nodes to each other.
The exposed problem exists in a wireless system which employ a carrier sense multiple access/collision avoidance (CSMA/CA) mechanism for channel access, such as Institute of Electrical and Electronics Engineers (IEEE) 802.11, 802.15.4, 802.15.6, and so on. When this exposed node problem happens, a media access protocol (MAC) mechanism, such as CSMA/CA mechanism, cannot function efficiently.
It should be noted that the above description of the background is merely provided for clear and complete explanation of this disclosure and for easy understanding by those skilled in the art. And it should not be understood that the above technical solution is known to those skilled in the art as it is described in the background of this disclosure.